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Under Scrutiny: Four 1200 dpi Scanners

Color Fidelity

Scores for color fidelity were obtained from the following test:

We scanned a grayscale consisting of 20 shades ranging from white to gray (coordinates 0 x 255) to pure black (19 on the horizontal axis, 0 on the vertical axis). Each shade is composed of the primary colors red, green, and blue. Once the pattern had been scanned, we broke it down into images in red, green and blue, and then we compared them with the theoretical values. A perfectly calibrated scanner would produce an RGB image of gray no. 10 with equal value and thus equivalent to 121.

In each of the following graphics, the white line represents the ideal, theoretical line. The red line records the red components of the scanned pattern. The green line represents the green component, and the blue line represents the blue component.

How Should The Curves Be Interpreted?

The further the RGB curves are from the white line, the greater the color changes made by the scanner.

If the RGB points are below the theoretical white point, the scanned dot is darker than the original. If the RGB dots are above the white point, then the scanned area is lighter than it ought to be.

Finally, the scanned pattern was in perfect gray, and the RGB elements for each point were supposed to be equal. Thus, the RGB curves ought to be perfectly superimposed.

In the case of the Astra 4500, at dot 10, the red dot is lower than the blue and green dots, indicating a tendency in the scanner to add too much red to this gray, with a risk that all the images will be slightly redder than they ought to be in other patterns.

The D1250U2 was the winner, with RGB curves that were almost perfectly superimposed.

The color balance (which indicates whether the RGB curves are superimposed or not) is 9.14 / 10 .

The RGB curves are quite close to the white line. There is thus a good degree of color compliance: 6.94 / 10 . The further the distance between the RGB curves and the white line, the lower the grade.

Hence the average final grade between the two grades of 8.1 / 10 as shown in the table at the top of the page.